Hi Greg,
Greg Keith wrote:
> The first part of this is not exactly a TDS question, but the second
> part is...
>
> We have had some recent complaints that the NetCDF data we serve using
> THREDDS from http://www.cdc.noaa.gov/thredds/ cannot be imported
> successfully into ArcGIS. In contrast to our installation, we are told
> that the NetCDF files served from the NCDC NOMADS THREDDS server at
> http://nomads.ncdc.noaa.gov/thredds/catalog/narr/catalog.html import
> successfully.
>
> I am wondering if the reason why is because the metadata in the NetCDF
> files we serve using THREDDS adheres to the CF 1.0 conventions, and it
> is lacking the more full-featured grid mapping attributes added in
> later CF versions, specifically the "grid_mapping_name =
> latitude_longitude" grid mapping I see documented in the CF 1.4
> conventions
> (http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.4/cf-conventions.html#appendix-grid-mappings).
Most of the grid mapping details were in CF 1.0 though some
datum/ellipsoid details where added in CF 1.2 and some projection types
were added in 1.2 and 1.4.
I don't know which version of CF is targeted by ArcGIS.
> However, I thought that if ArcGIS assumes the WGS-84 datum where
> projection is not specified, it would default to lat/long when
> importing the file...
I'm also not sure what kinds of assumptions they make if the data is
missing any of the information they require.
> The second part of this question IS a THREDDS-specific question - I
> see, for example with the NCDCD NOMADS TDS NARR files (for example
> http://nomads.ncdc.noaa.gov/thredds/ncss/grid/narr/200902/20090223/narr-b_221_20090223_0600_000.grb/dataset.html),
> that NCDC is serving GRIB files and then using the NetCDF Subset
> Service to allow the user to add required variables ("Add Lat/Lon to
> file" may be the crucial piece missing in our setup for imports into
> ArcGIS). However, I don't understand from looking at the NetCDF Subset
> Service docs what enables this interface - is it a config setting in
> TDS, more comprehensive metadata in the files we serve, both?
The NCSS service does not need to be enabled in the threddsConfig.xml
file but it does need to be specified for the datasets that you want to
be served by the NCSS. By which I mean, add a NCSS service element to
your catalog and have your dataset(s) reference that service from their
child serviceName element, or inherit a reference to that service.
(Note: The NCSS service only works for gridded datasets.)
The NCSS service must look like the following (though the name can be
changed):
<service name="ncss" serviceType="NetcdfSubset" base="/thredds/ncss/" />
which isn't well advertised but can be found in our Tutorial pages:
http://www.unidata.ucar.edu/projects/THREDDS/tech/tutorial
http://www.unidata.ucar.edu/projects/THREDDS/tech/tutorial/ConfigCatalogs.html#ConfigCats
There's more detail on the NCSS web interface at:
http://www.unidata.ucar.edu/projects/THREDDS/tech/interfaceSpec/NetcdfSubsetService.html
Ethan
>
> Thanks, Greg
>
